Submersible pumping systems and methods for deep well applications

ABSTRACT

Submersible pumping systems, devices and methods for extracting liquids in deep well applications are disclosed. In the various embodiments, a submersible pumping system includes a power supply and a power converter coupled to the power supply. A subsurface unit may be coupled to the power converter and positioned in the well. The subsurface unit may include a subsurface controller, a motor and a pump portion operably coupled to the subsurface controller. The pump portion may further include a front shroud having an inlet, and a back shroud sealably coupled to the front shroud to define a volume. An orifice fluidly communicates with the volume and an annular fluid discharge space disposed about the subsurface unit. An impeller operably coupled to the motor and positioned within the volume may transport a liquid from the inlet to the annular fluid discharge space.

TECHNICAL FIELD

The present invention relates generally to fluid transfer devices and methods, and more particularly, to submersible pumping systems, devices and methods for extracting liquids in deep well applications.

BACKGROUND

Submersible pumps are typically employed in sub-surface pumping applications where it is desired to remove liquids from relatively deep well locations. A centrifugal pump is typically employed in such applications, since it may be readily configured to provide a relatively high pumping head while providing a desired liquid flow rate at a surface location. Submersible centrifugal pumps of conventional design typically include a series of vertically stacked radial impellers in order to provide the desired lift from the well. The impeller stack is generally rotationally coupled to an electric motor that that may be located at the sub-surface location, and coupled to the centrifugal pump by a shaft that extends from the centrifugal pump to the motor.

Submersible pumps are also commonly used in well-sampling and monitoring applications. In such applications, however, the submersible pump must be suitably dimensioned to be removably positioned in a bore hole of relatively small diameter (e.g., approximately one to four inches in diameter), while providing acceptable performance over a wide range of well depths and flow rates. In selected instances, the submersible pump may be operated intermittently, so that the well is periodically sampled.

In the interest of reducing size, complexity and manufacturing costs, centrifugal pumps in well-sampling and monitoring applications generally employ a single impeller that is closely coupled to an electric motor that is positioned with a sealed enclosure. Accordingly, numerous difficulties are encountered in the design and operation of well-sampling and monitoring applications that are not present in larger multi-stage devices. For example, relatively long electrical lead lengths may introduce undesired transient electrical loading conditions that may adversely affect the motor, the power supply, or both.

Therefore, what is needed in the art are submersible pumping systems, apparatuses and methods that extracting liquids in deep well applications.

BRIEF DESCRIPTION OF THE DRAWINGS

The various embodiments of the present invention are described in detail below with reference to the following drawings.

FIG. 1 is a diagrammatic block view of a submersible pumping system, according to the various embodiments.

FIG. 2 is a diagrammatic block view of another submersible pumping system, according to the various embodiments.

FIG. 3 is a diagrammatic block view of a power converter according to the various embodiments.

FIG. 4 is a diagrammatic block view of another power converter according to the various embodiments.

FIG. 5 is a diagrammatic block view of a feedback system according to the various embodiments, which will be used to further describe the closed feedback loop previously discussed in connection with FIG. 2.

FIG. 6 is a diagrammatic block view of a subsurface unit according to the various embodiments.

FIG. 7 is a diagrammatic block view of a subsurface controller according to the various embodiments.

FIG. 8 is a graphical representation of a motor speed distribution according to the various embodiments.

FIG. 9 is a partial cross sectional view of a subsurface unit according to the various embodiments.

FIG. 10 is a frontal plan view of the front shroud of the centrifugal pump of FIG. 9.

FIG. 11 is a cross sectional view of the front shroud of FIG. 10.

FIG. 12 is a rear plan view of the front shroud of FIG. 10.

FIG. 13 is an expanded, partial cross sectional view of the front shroud of FIG. 10.

FIG. 14 is a frontal plan view of the impeller of FIG. 9.

FIG. 15 is a cross sectional view of the impeller of FIG. 14.

FIG. 16 is a frontal plan view of the back shroud of FIG. 9.

FIG. 17 is a cross sectional view of the back shroud of FIG. 16.

FIG. 18 is a flowchart that describes a method of removing a liquid from a well, according to the various embodiments.

FIG. 19 is a flowchart that describes a method of removing a liquid from a well, according to the various embodiments.

DETAILED DESCRIPTION

The present invention relates to submersible pumping systems, devices and methods for extraction of liquids in deep well applications. Many specific details of the various embodiments are set forth in the following description and in FIGS. 1 through 19 to provide a thorough understanding of such embodiments. One skilled in the art, however, will understand that the present invention may have additional embodiments, and that many of the various embodiments may be practiced without several of the details described in the following description.

FIG. 1 is a diagrammatic block view of a submersible pumping system 10, according to the various embodiments. The system 10 includes a subsurface unit 12 that is configured to be lowered into a bore hole 14 and to be at least partially immersed into a liquid 16 that is present in a lower portion of the bore hole 14. The subsurface unit 12 further includes a pump portion 18, a motor 20 that is operably coupled to the pump portion 18, and a subsurface controller 22 that is operable to control the motor 20. Briefly, and in general terms, the pump portion 18, the motor 20 and the subsurface controller 22 cooperatively permit the liquid 16 located in the lower portion of the bore hole 14 to be transferred to a position proximate to a ground surface location 24 through a liquid discharge conduit 26. The pump portion 18, the motor 20 and the subsurface controller 22 will be described in greater detail below.

The system 10 further includes a power supply 28 that is coupled to a power converter 30 that is, in turn, coupled by electrical leads 29 to the subsurface unit 12 to provide electrical energy to the unit 12. The power supply 28 may include any suitable alternating current (AC) or direct current (DC) source. For example, the power supply 28 may include a DC source, such as a storage battery, or an AC source, such as a conventional AC power distribution system. In other of the various embodiments, the power supply 28 may include an energy source that is suitable to supply either AC or DC power to the power converter 30 and the subsurface unit 12 when the system 10 is positioned at a remote location that disfavors the use of a storage batteries, and where conventional AC power is not available. For example, the power supply 28 may include an electrical generator that is coupled to a prime mover, such as an internal combustion engine, to provide either AC or DC power to the power converter 30. The power supply 28 may also include a wind turbine that is structured to generate rotational motion from atmospheric winds, and to impart the rotational motion to a generator that provides either AC or DC power. In still other of the various embodiments, the power supply 28 may include one or more photovoltaic panels that are structured to receive illumination (e.g., solar illumination) and convert the received illumination to an electrical current. In still other embodiments, power sources based upon electrochemical energy conversion may be used, such as a fuel cell, or other similar devices.

Still referring to FIG. 1, the power converter 30 is suitably configured to receive either AC or DC power from the power supply 28, and to suitably transform the received power to obtain a desired performance from the subsurface unit 12. For example, the power converter 30 may be configured to controllably alter a voltage or a current transferred to the subsurface unit 12 so that a desired flow rate is delivered through the liquid discharge conduit 26. Accordingly, the power converter 30 may be coupled to a control input 32 that is operable to set a voltage or current so that the desired flow rate is achieved. The control input 32 may be provided by an analog input, such as an analog voltage or current level, which may be manually set (e.g., by altering a potentiometer setting), or it may be a digital input, that may be provided by an external digital device (e.g., a digital computer) operably coupled to the power converter 30. In still another of the various embodiments, the control input 32 may be configured to control an operational time for the subsurface unit 12, so that the unit 12 may be intermittently operated. For example, the control input 32 may provide that the unit 12 is operated at predetermined times, which may be non-periodic, or periodic. Additionally, the control input 32 may provide for different flow rates during different operational periods. The power converter 30 will be described in greater detail below.

FIG. 2 is a diagrammatic block view of another submersible pumping system 40, according to the various embodiments. Many of the details shown in FIG. 2 have been previously described in detail, and in the interest of brevity, will not be discussed further. The system 40 includes a feedback system 42 (that includes a power converter, as previously described) that may be suitably coupled to a flow meter 44 so that signals received from the flow meter 44 may be used to at least partially control a flow rate delivered by the subsurface unit 12. The feedback system 42 and the flow meter 44 advantageously comprise a closed feedback loop that may cooperatively provide a relatively uniform flow rate from the subsurface unit 12. A suitable closed feedback system according to the various embodiments will be discussed in greater detail below.

With reference now to FIG. 3, a power converter 50 according to the various embodiments will now be discussed in detail. The power converter 50 includes a DC-to-DC converter 52 that is configured to be coupled to a DC power supply at input terminals 54, and to provide a selected DC output at output terminals 56. The DC-to-DC converter 52 may include a “buck-boost” device that is structured to accept an approximately constant input voltage V_(DC, IN) and to provide a variable output voltage V_(DC, OUT) that may range above or below the input voltage V_(DC, IN). For example, if the input voltage V_(DC, IN) is approximately about 12 volts, DC, then the DC-to-DC converter 50 may provide a V_(DC, OUT) that ranges between approximately about 0 volts, DC and approximately about 60 volts, DC. In another of the various embodiments, the DC-to-DC converter 50 may be a “boost” converter that is structured to accept an approximately constant input voltage V_(DC, IN) and to provide a variable output voltage V_(DC, OUT) that is greater than the input voltage V_(DC, IN). For example, if the input voltage V_(DC, IN) is approximately about 12 volts, DC, then the DC-to-DC converter 50 may provide a V_(DC, OUT) that ranges between approximately about 12 volts, DC and approximately about 60 volts, DC. In either case, the DC-to-DC converter 50 may be coupled to an input circuit 58 that is configured to receive the control input 32 and to provide a suitable output to the converter 50 so that a desired output voltage V_(DC, OUT) is provided.

The power converter 50 may also include an indication unit 60 that is operable to measure the output voltage V_(DC, OUT), and to display the value on a visual display 62. In another of the various embodiments, the indication unit may be configured to measure a current value delivered to the output terminals 56. In still another of the various embodiments, the indication unit 60 may be configured to measure an electrical power value delivered to the output terminals 56. In another of the various embodiments, the indication unit 60 may be configured to display a liquid flow rate.

FIG. 4 is a diagrammatic block view of another power converter 70 according to the various embodiments. Again, many of the details shown in FIG. 4 have been previously described in detail, and in the interest of brevity, will not be discussed further. The power converter 70 is configured to be coupled to an AC source 72, having an RMS input voltage V_(AC, IN). The AC source 72 may include a single phase source, or it may include a polyphase source. In either case, the AC source 72 may be coupled to an AC-to-DC converter 74 that is operable to convert a voltage received from the AC source 72 to a suitable DC voltage level. The AC-to-DC converter 74 may include, for example, a rectifier assembly. Although not shown in FIG. 4, if the AC source 72 is a polyphase source, the converter 74 may include conversion components (e.g., a rectifier assembly) that are arranged in parallel for the conversion of each phase.

The AC-to-DC converter 74 may be coupled to a DC-to-DC converter 52, as previously described. When the input voltage V_(AC, IN) includes one of a 120 v and a 208 v AC source, the DC-to-DC converter which may include a “buck” converter, so that the output voltage V_(DC, OUT) is reduced to a suitable level. In other embodiments, a boost converter, or a buck-boost converter may also be used.

FIG. 5 is a diagrammatic block view of a feedback system 80 according to the various embodiments, which will be used to further describe the closed feedback loop previously discussed in connection with FIG. 2. The system 80 includes a feedback unit 82 that further includes a comparator unit 84 that is coupled to a control mode unit 86. The comparator 84 is operable to receive the control input 32 and to receive a feedback input 88, and to generate an error signal e based upon a comparison of the received control input 32 and the feedback input 88. The feedback input 88 is received from the flow meter 44, that generates the feedback input 88 in response to a liquid flow 91 delivered by the subsurface unit 12 (as shown in FIG. 1 or FIG. 2). The error signal e may then be transferred to a control mode unit 86 that is configured to implement a specified control mode for the system 80. For example, the control mode may include one of a proportional (P) control mode, a derivative (D) control mode, a proportional-derivative (P-D) control mode, an integral (I) control mode, a proportional-integral (P-I) control mode, and a proportional-integral-derivative (P-I-D) control mode. Accordingly, the feedback unit 82 is operable to provide a suitably-corrected input value to a power converter 89, which may include one of the various embodiments shown in FIG. 3 and FIG. 4. One skilled in the art will readily appreciate that various components of the feedback unit 82 (e.g., the comparator 84 and the control mode unit 86) may be implemented using either analog or digital circuits, and may be further implemented in firmware, or entirely in software.

With reference now to FIG. 6, a subsurface unit 90 according to the various embodiments will now be discussed. The subsurface unit 90 includes a centrifugal pump 92 that is configured to fluidly communicate with a liquid 16 (as shown in FIG. 1) which may be present in the lower portion of the bore hole 14 (also shown in FIG. 1), and transfer the liquid 16 to the conduit 26 (also shown in FIG. 1). The centrifugal pump 92 will be discussed in greater detail below. The centrifugal pump 92 may be mechanically coupled to a motor 94 to impart a torque 96 to the centrifugal pump 92. In the various embodiments, the motor 94 may include a brushless, sensorless, polyphase motor.

The motor 94 may be conductively coupled to a subsurface controller 98 by a conductive assembly 100 that is structured to be removably coupled to at least one of the motor 94 and the subsurface controller 98. The assembly 100 may accordingly include a plurality of parallel conductive components that are each configured to couple a single phase to the polyphase motor 94. The subsurface controller 98 may, in turn, be coupled to one of the power converter 50, as shown in FIG. 3, and the power converter 70, as shown in FIG. 4. The subsurface controller 98 may be configured to provide polyphase power to the motor 94, provide power compensation, control a speed of the motor 94, or otherwise condition the polyphase power delivered to the motor 94. The subsurface controller will be discussed in greater detail below.

FIG. 7 is a diagrammatic block view of a subsurface controller 110 according to the various embodiments. The subsurface controller 110 may include a compensation circuit 112 that is coupled to one of the power converter 50, as shown in FIG. 3, and the power converter 70, as shown in FIG. 4. The compensation circuit 112 may include one or more capacitors that are suitably arranged to provide power compensation that addresses reactive effects introduced by the polyphase motor 94 and/or reactive and resistive effects introduced by electrical leads that couple the power converter 50, as shown in FIG. 3, and the power converter 70, as shown in FIG. 4, to the subsurface controller 110. Accordingly, the compensation circuit 112 may advantageously avoid instability in a polyphase motor controller 114 coupled to the compensation circuit 112. The polyphase motor controller 114 may include, for example, suitable inverter circuits to provide one or more AC phases to the motor 94. Additionally, the motor controller 114 may be configured to regulate a speed for the motor 94 by sensing a back electromotive force (EMF) developed by the motor 94 when a change in an armature speed of the motor 94 occurs. For example, the controller 114 may be configured to detect the back EMF, and to controllably alter at least one of a voltage and a current delivered to the motor 94 to return the motor 94 to a desired speed. The polyphase motor controller 114 may also be coupled to a motor speed controller 116 that is configured to control a rotational speed of the motor 94 when electrical power is initially applied to the motor 94, and that extends for a period of time until the motor reaches a full-speed value, as will be discussed in greater detail below.

With reference now also to FIG. 8, a motor speed distribution 120 according to the various embodiments is shown, which may be implemented by the motor speed controller 116. In one of the various embodiments, a motor speed distribution 122 is approximately linear, so that the speed of the motor 94 increases from stationary to a full speed value at a constant rate. Accordingly, upon being energized, the motor 94 reaches a maximum speed at a time T, which in an embodiment, may be approximately one to three seconds. In another of the various embodiments, a motor speed distribution 124 is approximately parabolic (e.g., a polynomial of second degree), so that the speed of the motor 94 increases at a variable rate upon being energized. In still another of the various embodiments, a motor speed distribution 126 may have still other shapes, such as a third-degree polynomial, so that the speed of the motor 94 increases at still another non-constant rate.

FIG. 9 is a partial cross sectional view of a subsurface unit 130 according to the various embodiments. As discussed previously in connection with FIG. 6, a centrifugal pump 132 may be mechanically coupled to the motor 94, which, in turn, receives electrical power from the subsurface controller 110. The centrifugal pump 132 includes a front shroud 134 and a back shroud 136 that are sealably coupled. The front shroud 134 may include a strainer 133 that is configured to prevent debris from entering the centrifugal pump 132, while the back shroud 136 may include a suitable shaft seal 135 to sealably restrict the liquid from contacting the motor 94. The front shroud 134 and the back shroud 136 cooperatively define a volume 140 that encloses an impeller 138 that is mechanically coupled to the motor 94. The volume 140 fluidly communicates with an orifice 142 that is configured to expel a liquid confined within the volume 140 when a torque is imparted to the impeller 138 by the motor 94. Various details of the centrifugal pump 132 will be discussed in greater detail below.

The subsurface unit 130 further includes a generally cylindrical inner housing 144 that may be sealably coupled to the back shroud 136, which may also be sealably coupled to an end cap 146. Accordingly, the back shroud 136, the inner housing 144 and the end cap 146 may cooperatively form a hermetically-sealed volume 148 that contains the motor 94 and the subsurface controller 110. A generally cylindrical outer housing 150 may be sealably coupled to the front shroud 134 and to the end cap 146 to define a generally annular fluid discharge space 152 between the inner housing 144 and the outer housing 150. The fluid discharge space 152 fluidly communicates with a fluid passage 154 formed in the end cap 146, that may further fluidly communicate with the liquid discharge conduit 26 through a suitable end fitting 156. The end cap 146 may also include suitable electrical feedthroughs 158 that permit the subsurface controller 110 and the motor 94 to be electrically coupled to one of the converters 50 and 70, as shown in detail in FIGS. 3 and 4, respectively.

With reference now to FIG. 10, a frontal plan view of the front shroud 134 of the centrifugal pump 132 of FIG. 9 is shown, that will be used to describe the front shroud 134 in greater detail. The strainer 133 includes a plurality of apertures 170 that may project through the housing 134 in an axial direction, and may also project through the front shroud 134 in a radial direction. Although a plurality of apertures 170 are shown, it is understood that other configurations are possible, and are also within the scope of the various embodiments. For example, a screen having a predetermined mesh size may also provide the strainer 133.

FIG. 11 is a cross sectional view of the front shroud 134 of FIG. 10, along the cross section 11-11 of FIG. 10. The plurality of apertures 170 permit fluid communication between a liquid 16 (see FIG. 1) and an inlet 172. The front shroud 134 may further include a conical inner portion 174 that adjoins the inlet 172. In the various embodiments, the conical inner portion 174 may include a taper angle α that may range between approximately about 30 degrees and approximately about 90 degrees. In another of the various embodiments, the taper angle α may range between approximately about 45 degrees and approximately about 60 degrees, although other values for the taper angle α may be used. The front shroud 134 may also include a circumferential land 176 that receives the outer housing 150 (as shown in FIG. 9), and a circumferential wall 178 that at least partially receives the back shroud 136 on an inner peripheral portion.

Referring now to FIG. 12, and with continuing reference to FIGS. 10 and 11, a rear plan view of the front shroud 134 is shown. As discussed briefly in connection with FIG. 9, an orifice 142 projects through the circumferential wall 178 and into the conical inner portion 174 of the front shroud 134 at a location 180. With reference now also to FIG. 13, an expanded, partial cross sectional view of the front shroud of FIG. 10 is shown, that will be used to describe the orifice 142 at the location 180 in greater detail. The orifice 142 approximately tangentially extends through the wall 178, and may include a constant diameter portion 182 and a tapered portion 184. The tapered portion 184 is generally conical in shape, having an included angle β. In the various embodiments, the included angle β may range between approximately five degrees, and approximately 50 degrees. In others of the various embodiments, the included angle β may range between approximately 15 degrees, and approximately 25 degrees, although other angular ranges may also be used. The constant diameter portion 182 may have any suitable diameter d, but in accordance with the various embodiments, the diameter d may range between approximately about 0.030 inches, and approximately about 0.120 inches.

FIG. 14 is a frontal plan view of the impeller 138 of FIG. 9, which will be used to describe various details of the impeller 138 in greater detail. The impeller 138 may include a disk 190 that supports a plurality of vanes 192 that extend outwardly from the disk 190. Although the impeller 138 shown in FIG. 14 includes six vanes 192, it is understood that the disk 190 may support more than six vanes 192, or even less than six vanes 192. Further, although the vanes 192 shown in FIG. 14 are generally straight, it is understood that the vanes 192 may include other shapes. For example, the vanes 192 may be backwardly curved, or even forwardly curved. The disk 190 may include a plurality of apertures 194 that project through the disk 190. The impeller 138 may also include an impeller hub 196 that is coupled to the disk 190 and suitably dimensioned to receive a shaft coupled to the motor 94 (as shown in FIG. 9). In the various embodiments, the hub 196 may be suitably dimensioned to fixably retain the impeller 138 on the shaft of the motor 94 by an interference fit. In other of the various embodiments, the impeller 138 may be coupled to a shaft of the motor 94 using mechanical fasteners, such as set screws, or other similar elements.

FIG. 15 is a cross sectional view of the impeller 138 of FIG. 14, along the cross section 15-15 of FIG. 14. The impeller hub 196 may be positioned on a shaft of the motor 94 so that a predetermined clearance distance l may be maintained between the vanes 192 and the front shroud 134. In the various embodiments, the clearance distance l may range between approximately about 0.005 inches and approximately about 0.040 inches. In other of the various embodiments, the clearance distance l may range between approximately about 0.008 inches and approximately about 0.020 inches.

FIG. 16 is a frontal plan view of the back shroud 136, which will be used to describe the back shroud 136 in greater detail. The back shroud 136 includes an inner recess 200 that is suitably dimensioned to accommodate the impeller hub 196 (as shown in FIG. 15). A shaft hole 202 extends through the back shroud 136 that permits the shaft portion of the motor 94 (as shown in FIG. 94) to engagably receive the impeller hub 196. An outer recess 204 extends into the back shroud 136 that is suitably dimensioned to receive a corresponding portion of the front shroud 134. Mutually spaced-apart protrusions 206 may extend outwardly from a peripheral edge of the back shroud 136 that receive and support the outer housing 150 as it engages the back shroud 136 to provide flow passages 208 that permit the orifice 142 (as shown in FIG. 9, and in greater detail in FIG. 13) to fluidly communicate with the annular fluid discharge space 152.

FIG. 17 is a cross sectional view of the back shroud 136 of FIG. 16, along the cross section 17-17 of FIG. 17. The back shroud 136 may further include a rear recess 210 that extends inwardly into the back shroud 136, and that is suitably dimensioned to receive the shaft seal 135 (as shown in FIG. 9) that restricts liquid movement into the volume 148 (as also shown in FIG. 9). The back shroud 136 may also include an outwardly extending land 205 that may be received by the front shroud 134 so that the land 205 is adjacent to the wall 178 (as shown in FIG. 11).

FIG. 18 is a flowchart that will be used to describe a method 230 of removing a liquid from a well, according to the various embodiments. With reference also again to FIGS. 1 and 2, the method 230 includes positioning a subsurface unit 12 in a bore hole 14, as shown at block 232. At block 234, the subsurface unit 12 is coupled to a power supply 28 and a power converter 30. At block 236, the motor 20 within the subsurface unit 12 is started using a selected motor speed distribution 120 (as shown in FIG. 8). For example, in one of the various embodiments, the motor speed distribution 120 is a linear distribution, wherein the motor 20 is accelerated to 100 percent of a desired full speed setting within approximately four seconds. At block 238, a desired steady state speed for the motor 20 is set by controlling a control input 32 to the power converter 30. At block 240, a variation in the steady-state speed is detected by the subsurface controller 22 by sensing a back EMF from the motor 20. Based upon the sensed back EMF, the subsurface controller 22 corrects at least one of a current and a voltage delivered to the motor 20 to return to the desired steady state speed.

FIG. 19 is a flowchart that will be used to describe another method 250 of removing a liquid from a well, according to the various embodiments. With reference still also to FIGS. 1 and 2, the method 250 includes positioning a subsurface unit 12 in a bore hole 14, as shown at block 252. At block 254, the subsurface unit 12 is coupled to a power supply 28, feedback system 42 and a flow meter 44. At block 256, a desired flow rate to be delivered by the subsurface unit 12 is selected. The flow rate may be selected, for example, by identifying a rate at which liquid must be removed in order to properly sample the bore hole 14, or by identifying a rate that will maintain a dewatered state in the bore hole 14. At block 258, a speed for the motor 20 is set that will deliver the desired flow rate. The speed may be set by controlling a control input 32 to the feedback system 42. As discussed previously, the motor 20 within the subsurface unit 12 may be started using a selected motor speed distribution 120 (as shown in FIG. 8). At block 260, the flow rate delivered by the subsurface unit 12 may be measured by the flow meter 44. At block 270, the measured flow rate is compared to the set flow rate (from block 258). If the measured flow rate differs from the desired flow rate, the feedback system 42 appropriately corrects at least one of a voltage and a current delivered to the motor 20 to attain the desired flow rate, as shown in block 270. If the measured flow rate does not differ from the desired flow rate, then the method 250 returns to block 260.

While the various embodiments of the invention have been illustrated and described, as noted above, many changes can be made without departing from the scope of this disclosure. Thus, although specific embodiments have been illustrated and described herein, it should be appreciated that any arrangement calculated to achieve the same purpose may be substituted for the specific embodiments shown. This disclosure is intended to cover any and all adaptations or variations of various embodiments. Combinations of the above embodiments, and other embodiments not specifically described herein, will be apparent to those of skill in the art upon reviewing the above description.

Further, the accompanying drawings that form a part hereof show by way of illustration and not of limitation, specific embodiments in which the subject matter may be practiced. The embodiments illustrated are described in sufficient detail to enable those skilled in the art to practice the teachings disclosed herein. Other embodiments may be utilized and derived therefrom, such that structural and logical substitutions and changes may be made without departing from the scope of this disclosure. This Detailed Description, therefore, is not to be taken in a limiting sense, and the scope of various embodiments is defined only by the appended claims, along with the full range of equivalents to which such claims are entitled.

The Abstract of the Disclosure is provided to comply with 37 C.F.R. §1.72(b), requiring an abstract that will allow the reader to quickly ascertain the nature of the technical disclosure. It is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims. In addition, in the foregoing Detailed Description, it can be seen that various features may be grouped together in a single embodiment for the purpose of streamlining the disclosure. This method of disclosure is not to be interpreted as reflecting an intention that the claimed embodiments require more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive subject matter lies in less than all features of a single disclosed embodiment. Thus the following claims are hereby incorporated into the Detailed Description, with each claim standing on its own as a separate embodiment. 

1. A submersible pumping system for a well, comprising: a power supply; a power converter coupled to the power supply; and a subsurface unit coupled to the power converter and configured to be positioned in the well remote from the power supply and the power converter, wherein the subsurface unit includes a subsurface controller, and a motor and a pump portion operably coupled to the subsurface controller, the pump portion further comprising: a front shroud having an inlet; a back shroud sealably coupled to the front shroud to define a volume there between; an orifice that fluidly communicates with the volume and an annular fluid discharge space at least partially disposed about the subsurface unit; and an impeller operably coupled to the motor and positioned within the volume to transport a liquid from the inlet to the annular fluid discharge space.
 2. The system of claim 1, wherein the front shroud includes an axially disposed conical inner portion having a taper angle that ranges between approximately 45 degrees and approximately 60 degrees.
 3. The system of claim 1, wherein the front shroud comprises a strainer fluidly coupled to the inlet that is configured to restrict the entry of solid material into the volume.
 4. The system of claim 1, wherein the orifice comprises a constant diameter portion and a tapered portion coupled to the constant diameter portion, the tapered portion having an included angle that ranges between approximately five degrees, and approximately 50 degrees.
 5. The system of claim 4, wherein the constant diameter portion comprises a diameter that ranges between approximately 0.030 inches, and approximately 0.120 inches.
 6. The system of claim 1, wherein the impeller comprises a planar and circular disk that supports a plurality of outwardly extending vanes, and a centrally disposed impeller hub configured to be coupled to the motor.
 7. The system of claim 6, wherein the disk comprises a plurality of apertures extending through the disk and positioned between the outwardly extending vanes.
 8. The system of claim 6, wherein the outwardly extending vanes are spaced apart from the front shroud by a clearance distance that ranges between approximately 0.005 inch and approximately 0.040 inch.
 9. The system of claim 6, wherein the outwardly extending vanes are inclined at an angle that ranges between approximately 45 degrees and approximately 60 degrees.
 10. The system of claim 6, wherein the impeller hub is configured to fixedly retain a shaft extending from the motor using an interference fit.
 11. The system of claim 1, wherein the motor comprises a polyphase, brushless and sensor less DC motor.
 12. A submersible pumping system for a well, comprising: a power supply; a power converter coupled to the power supply; and a subsurface unit coupled to the power converter and configured to be positioned in the well remote from the power supply and the power converter, wherein the subsurface unit includes a pump portion and a motor operably coupled to the pump portion, and a subsurface controller, the subsurface controller further comprising: a power compensation circuit operable to receive electrical power from the power converter configured to reduce at least one of a reactance introduced by the motor and reactive and resistive effects introduced by electrical leads coupling the power converter to the subsurface unit; a motor controller coupled to the power compensation circuit that is configured to convert electrical power received from the power compensation circuit to polyphase electrical power that is communicated to the motor; and a motor speed controller configured to control a rotational speed of the motor when the polyphase electrical power is first applied to the motor.
 13. The system of claim 12, wherein the power supply comprises one of an alternating current (AC) source and a direct current (DC) source.
 14. The system of claim 13, wherein the DC source comprises one of a storage battery, one or more photovoltaic panels, and a fuel cell device.
 15. The system of claim 13, wherein the power converter comprises a DC-to DC converter configured to receive a DC voltage at a first voltage level, and convert the DC voltage to a second voltage level.
 16. The system of claim 15, wherein the DC-to-DC converter comprises one of a buck-boost converter, a boost converter and a buck converter.
 17. The system of claim 15, wherein the DC-to-DC converter is coupled to an AC-to-DC converter that receives an AC voltage from the power supply, and converts the AC voltage to a DC voltage.
 18. The system of claim 12, wherein the power compensation circuit comprises one or more capacitors operably coupled to the power converter and the motor controller.
 19. The system of claim 12, wherein the motor controller comprises at least one inverter circuit configured to receive a DC voltage, and to convert the DC voltage to an AC voltage.
 20. The system of claim 12, wherein the motor controller comprises a speed sensing circuit that is operable to sense a back electromotive force from the motor and to regulate a speed of the motor based upon the sensed electromotive force.
 21. The system of claim 12, wherein the motor speed controller is configured to provide a motor speed distribution that is implemented during a time period that extends from a motor start value to a maximum speed value.
 22. The system of claim 21, wherein the time period is approximately one to three seconds.
 23. The system of claim 21, wherein the motor speed distribution extends linearly during the time period.
 24. The system of claim 21, wherein the motor speed distribution comprises one of a second-degree speed distribution and a third-degree speed distribution.
 25. A submersible pumping system for a well, comprising: a power supply; a feedback system coupled to the power supply; and a subsurface unit coupled to the feedback system and configured to be positioned in the well remote from the power supply and the feedback system, wherein the subsurface unit includes at least a pump portion and a motor operably coupled to the pump portion, the pump portion being operable to transport a volume of a liquid from the well to a flow meter, the feedback system further comprising: a control mode unit configured to implement a predetermined control mode; a power converter coupled to the control mode unit that is configured to receive electrical power from the power supply, and to controllably provide electrical power to the subsurface unit based upon an out\put from the control mode unit; and a comparator that receives a feedback signal from the flow meter that provides an error signal to the control mode unit based upon a comparison of the feedback signal and a desired flow value.
 26. The system of claim 25, wherein the control mode unit is configured to implement one of a proportional (P) control mode, a derivative (D) control mode, a proportional-derivative (P-D) control mode, an integral (I) control mode, a proportional-integral (P-I) control mode, and a proportional-integral-derivative (P-I-D) control mode.
 27. The system of claim 25, wherein the power converter comprises a DC-to DC converter configured to receive a DC voltage at a first voltage level, and convert the DC voltage to a second voltage level.
 28. The system of claim 27, wherein the DC-to-DC converter comprises one of a buck-boost converter, a boost converter and a buck converter.
 29. The system of claim 25, wherein the DC-to-DC converter is coupled to an AC-to-DC converter that receives an AC voltage from the power supply, and converts the AC voltage to a DC voltage.
 30. The system of claim 29, wherein the AC-to-DC converter comprises a rectifier circuit.
 31. A method of removing a liquid from a well, comprising: positioning a subsurface unit into a well, the subsurface unit including at least a pump portion coupled to a motor configured to impart a rotational motion to the pump portion; coupling the subsurface unit to a power supply and a power converter configured to controllably provide electrical power to the subsurface unit; and starting the motor using a selected motor speed distribution.
 32. The method of claim 31, wherein starting the motor using a selected motor speed distribution comprises implementing the motor speed distribution over a time period that ranges between approximately one to three seconds.
 33. The method of claim 31, wherein starting the motor using a selected motor speed distribution comprises a linear motor speed distribution.
 34. The method of claim 31, wherein starting the motor using a selected motor speed distribution comprises a parabolic motor speed distribution.
 35. The method of claim 31, wherein starting the motor using a selected motor speed distribution comprises a motor speed distribution conforming to a third-order polynomial.
 36. The method of claim 31, further comprising: setting a desired speed for steady-state motor operation; detecting a variation in the steady-state motor operation by sensing a back electromotive force from the motor; and correcting at least one of a voltage and a current delivered to the motor to return the motor to the desired speed.
 37. The method of claim 36, wherein setting a desired speed for steady-state motor operation comprises providing a control input to the power converter.
 38. A method of removing a liquid from a well, comprising: positioning a subsurface unit into a well, the subsurface unit including at least a pump portion and a motor coupled to the pump portion, the subsurface unit being configured to transport a liquid from the well to a surface location; coupling the subsurface unit to a power supply and a feedback system configured to controllably provide electrical power to the subsurface unit; selecting a desired flow rate to be delivered by the subsurface unit; setting a speed for the motor that delivers the desired flow rate; measuring a delivered flow rate; and if the delivered flow rate differs from the desired flow rate, then correcting the speed to attain the desired flow rate. 